For operation in harsh environments, it is good practice to use angle sensors based on magnetic principles. They cover a large temperature range from 50 degrees to 170 degrees Celsius, show practically no wear, and are robust against many kinds of contaminations. Automotive applications reach from small angular excursions of a few (angular) degrees (as used, e.g., in torque measurement) to medium angular excursions of 30 to 120 degrees (as used, e.g., in headlight levelling or throttle valve positioning) to complete 360 degree detection in motor position sensing and even to multi-turn detection for steering wheels. Particularly for angle ranges exceeding 180 degrees the most common systems use a small permanent magnet attached to the end surface of the rotating shaft. The magnetization is usually perpendicular to the rotation axis thus giving rise to a magnetic field, which is thus predominantly perpendicular to this axis. A magnetic field sensor is placed in front of the magnet. If the axis rotates the magnetic field also rotates and the rotation can be detected by the magnetic field sensor.
In practical implementations, the magnetic field generated by the permanent magnet used in the rotary encoder can be distorted by undesired external magnetic fields. Without countermeasures such distortion will results in a deteriorated measurement of the angular position or speed of the shaft. Thus, there is a need for rotary encoders which have a reduced sensitivity with regard to external magnetic fields in order to improve the accuracy of the encoder.